I think it's more about getting their pro careers started while they're still teenagers. After three years of college, most players are 21 or 22 years old and when they reach triple A minor league baseball, they're 25 or so competing with teenagers right out of HS.
By the time they get to the show, they're on their late 20's. Now if they're a phenom like Detmers who played only a year and a half of minor league baseball, those three years at college were good, but if it takes several years to reach the big leagues, you might wish you had those college years back.
Players like Corey Ray, Devin Mann, and Josh Stowers still are working to make the big show and all of them are counting the years to get there. Then there's Drew Ellis and Nic Solak who have tasted the big leagues but are now back at AAA.
Money is always a factor, especially now in the era of inflation, but if I were a 18 year old HS star, my motivation would be to get started professionally as soon as I can so I'm not 27 before I see the big leagues.